Sulphuric acid and bromine give with digitalin a red, and with digitalein a violet coloration, which, on the addition of water, change respectively into emerald and light green. This, the most important chemical test we possess, is sometimes called Grandeau’s test; it is not of great delicacy, the limit being about ·1 mgrm.
§ 536. Pharmaceutical Preparations of Digitalin.—Digitalin itself is officinal in the French, Belgium, Portuguese, Russian, Spanish, and Austrian pharmacopœias. It is prepared in our own by making a strong tincture of the leaves at 120° F.; the spirit is then evaporated off, and the extract heated with acetic acid, decolorised by animal charcoal, and filtered. After neutralisation with ammonia, the digitalin is precipitated with tannin, and the tannate of digitalin resolved into tannate of lead and free digitalin, by rubbing it with oxide of lead and spirit.
Digitalis leaf is officinal in most of the pharmacopœias.
Tincture of digitalis is officinal in our own and all the Continental pharmacopœias, and an ethereal tincture is used in France and Germany.
An Acetum digitalis is officinal in the Netherlands and Germany; an extract and infusion are also used to some extent.
With regard to the nature of the active principle in these different preparations, according to Dragendorff, digitonin and digitalein are most plentiful in the acetic and aqueous preparations; whilst in the alcoholic, digitalin, digitoxin, and digitalein are present.
According to Schmiedeberg, commercial digitalin contains, in addition to digitoxin, digitonin, digitalin, and digitalein; of these, digitonin is greatest in amount.[562]
[562] H. Kiliani, Ber., xxiii.